1. Field of the Invention
The present invention relates to a structure of a zoom lens barrel, and more specifically relates to a structure of a zoom lens barrel for moving a first lens frame along an optical axis by rotation of a cam ring which is driven to rotate, wherein the first lens frame supports the frontmost lens group among a plurality of lens groups of the zoom lens barrel.
2. Description of the Related Art
In conventional zoom lens barrels, it is often the case that a first lens frame which supports the first lens group (frontmost lens group) among a plurality of lens groups of the zoom lens barrel is moved along an optical axis by rotation of a cam ring which is driven to rotate. In the case where a zooming adjustment (which is an adjustment operation that is carried out in a manufacturing process of the zoom lens barrel as needed) is carried out by moving the second lens group positioned behind the first lens group relative to the first lens group, it is generally the case that an opening for this zooming adjustment is formed on the first lens frame while an independent light-shield exterior ring is fitted on the first lens frame to cover the opening in a light-tight fashion. This light-shield exterior ring is simply fixed to the first lens frame in conventional zoom lens barrels.
The present invention provides an improved structure of a zoom lens barrel for moving the first lens frame along an optical axis by rotation of a cam ring which is driven to rotate, wherein the structure provides a light-shield exterior ring so as to be multi-functional.
According to an aspect of the present invention, a zoom lens barrel is provided, including a cam ring which is driven to rotate; a first lens frame which is positioned around the cam ring to be guided linearly along an optical axis, the first lens frame supporting a frontmost lens group of a zoom lens system; a light-shield exterior ring which is positioned around the first lens frame; a first outer cam groove and a second outer cam groove which are formed on an outer peripheral surface of the cam ring, each the first and second cam grooves including a zooming range for performing a zooming operation of the zoom lens system; and a first cam follower formed on the first lens frame, the first cam follower being engaged in the first outer cam groove; a second cam follower formed on the light-shield exterior ring, the second cam follower being engaged in the second outer cam groove through a linear guide slot which is elongated in a direction parallel to the optical axis, which is formed on the first lens frame. The first outer cam groove and the second outer cam groove are shaped so as to move the first lens frame and the light-shield exterior ring in the same moving path in the zooming ranges thereof.
It is desirable for the zoom lens barrel to include a lens barrier unit including at least one barrier blade, wherein the lens barrier unit is supported by the light-shield exterior ring at a front end thereof, and retracting ranges of the first outer cam groove and the second outer cam groove are shaped so that the light-shield exterior ring advances from a photographing position thereof relative to the first lens frame to position the lens barrier unit in front of the frontmost lens group without the lens barrier unit interfering with the frontmost lens group when the zoom lens barrel is retracted to a retracted position thereof.
It is desirable for the first lens frame to include an outer ring portion, an inner ring portion and a flange wall by which a front end of the outer ring portion and a front end of the inner ring portion are connected, and the cam ring to be positioned between the outer ring portion and the inner ring portion.
It is desirable for the zoom lens barrel to include a second lens frame which is positioned inside the inner ring portion, and is guided linearly along the optical axis, wherein at least one opening, through which the position of a lens group supported by the second lens frame in the optical axis direction, can be adjusted is formed on the first lens frame.
It is desirable for the zoom lens barrel to include a biasing member, positioned between the first lens frame and the light-shield exterior ring, for biasing the light-shield exterior ring forward relative to the first lens frame.
It is desirable for the biasing device to be a compression coil spring.
The opening can include at least one outer opening formed on the outer ring portion, and at least one inner opening formed on the inner ring portion. The outer opening and the inner opening are aligned in a radial direction of the zoom lens barrel.
It is desirable for the zoom lens barrel to include a stationary barrel having a female helicoid formed on an inner peripheral surface of the stationary barrel. A male helicoid is formed on an outer peripheral surface of the cam ring to be engaged with the female helicoid. A spur gear which is engaged with a drive pinion is formed on thread of the male helicoid.
It is desirable for the zoom lens barrel to include a second lens frame which is positioned inside the inner ring portion, is guided linearly along the optical axis, and includes a third cam follower; and an inner cam groove formed on an inner peripheral surface of the cam ring so that the third cam follower is engaged in the third cam groove.
It is desirable for the distance in the optical axis direction between said first cam groove and of said second cam groove changes from a predetermined position within a range before said zoom range.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 2003-028631 (filed on Feb. 5, 2003) which is expressly incorporated herein by reference in its entirety.